[PATCH 13/20] drm/bridge: Add RGB to VGA bridge support
maxime.ripard at free-electrons.com
Thu May 26 02:38:12 PDT 2016
On Mon, May 16, 2016 at 09:07:18AM -0500, Rob Herring wrote:
> On Mon, May 16, 2016 at 7:47 AM, Maxime Ripard
> <maxime.ripard at free-electrons.com> wrote:
> > Some boards have an entirely passive RGB to VGA bridge, based on either
> > DACs or resistor ladders.
> > Those might or might not have an i2c bus routed to the VGA connector in
> > order to access the screen EDIDs.
> > Add a bridge that doesn't do anything but expose the modes available on the
> > screen, either based on the EDIDs if available, or based on the XGA
> > standards.
> > Signed-off-by: Maxime Ripard <maxime.ripard at free-electrons.com>
> > ---
> > .../bindings/display/bridge/dumb-vga.txt | 40 +++++
> > drivers/gpu/drm/bridge/Kconfig | 6 +
> > drivers/gpu/drm/bridge/Makefile | 1 +
> > drivers/gpu/drm/bridge/dumb-vga.c | 186 +++++++++++++++++++++
> > 4 files changed, 233 insertions(+)
> > create mode 100644 Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
> > create mode 100644 drivers/gpu/drm/bridge/dumb-vga.c
> > diff --git a/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
> > new file mode 100644
> > index 000000000000..757f04de97f3
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
> > @@ -0,0 +1,40 @@
> > +Passive RGB to VGA bridge
> > +-------------------------
> > +
> > +This binding is aimed for entirely passive RGB to VGA bridges that do not
> > +require any configuration.
> No reset or enable lines or regulators?
On the three designs I've seen:
- One doesn't need any of these
- One has a GPIO enable pin but with it's resistor not populated
- One has a regulator controlled by a GPIO
So I guess in most cases, we don't need anything, but we still might
to cover all cases.
> > +
> > +Required properties:
> > +
> > +- compatible: Should be "dumb-vga-bridge"
> > +
> > +Optional properties:
> > +
> > +- ddc-i2c-bus: phandle to the i2c bus used to communicate with the monitor
> The i2c bus is a property of the connector, not the bridge chip, so it
> belongs in a VGA connector node (which we already have binding for).
> I think for the really "dumb" (or transparent case), you should only
> have a connector. For anything more complex, then you should have both
> a DAC and connector node.
So, in essence, something like:
> On the driver side, I think we could handle multiple connectors with a
> single driver. Ideally, that would work with any DRM driver that has a
> connector node.
I'm not sure what you mean by that. I really think it should be a
separate driver in order to share the common code that so far the
current implementations put in some driver specific code (even though
it might be completely generic).
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
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